Spatiotemporal\nVariation in Dissolved, Bioavailable,\nand Particulate Elements and the Abundance of Harmful Algae in Grand\nLake

Harmful algal blooms (HABs) are often linked to the increased\nloading\nof limiting nutrients such as nitrogen and phosphorus. Little is known\nabout the relevance of other biogenic elements, the supplies of which\nare spatiotemporally heterogeneous, on HABs. We measured the dissolved,\nbioavailable, and particulate concentrations of 26 elements at four\nlocations draining different catchments of a large reservoir during\nthree seasons, in addition to the total abundance of phytoplankton\nand % of cyanobacteria. Finally, we manipulated a key element (Fe)\nin microcosms to test its effect on the community. Phytoplankton abundance\nand community structure varied spatiotemporally, with minimal variation\nin N/P. The variation in environmental supplies of several other elements\nwas correlated with phytoplankton abundance, as well as up to 3 orders\nof magnitude differences in cyanobacterial yield. Bioassays manipulating\nFe impacted total phytoplankton as well as the abundance of cyanobacteria,\nwith Fe-chelated treatments resulting in a significant decline in\nphytoplankton as well as cyanobacterial yield. In summary, we found\nsubstantial heterogeneity in elemental supplies that are relevant\nto the phytoplankton community. Exploring the relevance of the entire\nsystem of elements in the context of HABs may be more rewarding than\nstudies emphasizing a subset of elements.